Arrangement for shifting overs step switches on transformers under load



Nov. 26, 1963 J. BUHLER ARRANGEMENT FOR SHIFTING OVER STEP SWITCHES ON TRANSFORMERS UNDER LOAD 2 Sheets-Shet 1 Filed March 23, 1962 Karl, J 55%? Nov. 26, 1963 3,112,438

K. J. BUHLER ARRANGEMENT FOR SHIFTING OVER STEP SWITCHES Filed March 23, 1962 ON TRANSFORMERS UNDER LOAD 2 Sheets-Sheet 2 INVENTOR. Karl J B U hler BY 12%, JJ%@& PM.

United States Patent 3,112,438 ARRANGEMENT FQR SPTFTHNG OVER STEP SWITCHES 0N TRANSFORMERS UNDER LQAD Karl I. Biihler, Nusshaumen, Switzerland, assignor to Alrtiengesellschatt Brown, Beveri dz (lie, Baden, Switzerland, a ioint-stoclr company Filed Mar. 23, 1962, Ser. No. 182,040 Claims priority, application Switzerland Mar. 28, 1961 2 Claims. (Cl. 32.3-43.5)

This invention relates to tap-changing apparatus for transformer windings and more particularly to an improved apparatus of this kind for changing the taps without disconnecting the load from the transformer.

It is known to use load switches in conjunction with tap-changing switches for changing over from one tap to another in an uninterrupted manner. These operate by means of switch-over iinpedances and switch contacts. In the known types of devices, considerable switching arcs are involved, especially at high outputs, and these entail serious side effects such as detrioration of the contacts themselves, decomposition of the arc quenching agent, dirtying, gas formation, etc. In addition, it is known to replace the necessary switch-over contacts in part by current gates connected in anti-parallel so as to conduct in opposite current directions. For these current gates have been used gas-filled discharge tubes, particularly those with ignition pin control such as ignitrons, transistors, semi-conductor thyratrons, and cold cathode tubes. The control for such current gates requires, in most cases, outside current sources and this is especially disadvantageous when the load switch operates at a high voltage as in the case of step up switches, using high-tension transformers. In addition, control contacts for these current gates are necessary, which is likewise undesirable.

The present invention provides an improved arrangement for tap-changing on transformers under load by means of a main switch, the tap-changing taking place with current gates connected in anti parallel, as well as with auxiliary contacts which are mechanically coupled with the operating mechanism for the movable contacts of the main switch.

More particularly, the invention is characterized by use of an impulse generator for control of the current gates, this impulse generator including a rotor element which is mechanically coupled to the main switch so as to rotate each time the movable element of the main switch is actuated and a stator element including coils in which voltages are induced upon rotation of the rotor. These stator coils with rectifiers wired in series therewith produce the ignition voltage impulses for the current gates and the arrangement is such that the movable contact of the main switch is connected to the stationary contacts thereof on the one hand across the current gates connected in series with a commutation switch, and on the other hand across a resistance, a resistance switch and a preselector switch all of which are series connected. Connected in parallel with the anti-parallel arranged current gates are two current gate switches connected in series, and the movable contacts of these current gate switches as well as the movable contacts of the commutation switch and the resistance switch are likewise mechanically coupled to the main switch so as to be actuated simultaneously with actuation of the movable contact of the main switch. The result is characterized in substantially arc-free operation of the main switch used in conjunction with the tapchanging on the transformer winding.

The invention will become more clearly understood from the following detailed description of two embodiments thereof and from the accompanying drawings in PhllZAdd Patented Nov. 26, 1963 "ice which FEGS. l and 2 represent respectively schematic circuit diagrams of the two embodiments.

With reference now to FIG. 1, the step-up transformer is designated by 31 and the taps of its regulating winding are indicated by Ilia to die. A contact rail 32 is provided for a slidable contact member 32a which establishes contact between this rail and the taps 31a, 31c and 310 in a selective manner. Similarly, a second contact rail 33 is provided for slidable contact member 3301 which establishes selective contact with taps 31b and 31a. The main switch, shown at 34, includes a movable contact member 34c and two stationary contact members 34a and 34b. Stationary contact 34a is connected to contact rail 32 and stationary contact 34b is connected to contact rail 33. The object of the invention is to make the switchover of the main switch 34 take place without current. in the short time permitted for the switching over, the current flows across the apparatus now to be described and which constitutes the invention.

For actuating the movable contact 34c of the main switch 3d, a drive indicated generally by block 43, e.g. a pneumatic cylinder, is provided. Two current gates 35, 36 arranged in anti-parallel are connected at one side to the movable contact member 34c of the main switch and at the other side to the stationary contacts 34a, 34b. For controlling conduction of the current gates 35, 36, the invention provides an impulse generator 37 which has a stator 3% and a rotor 37]). The rotor 37b which includes permanent magnets or which in the alternative can be provided with an electrically energized coil to produce the magnetic flux, is mechanically coupled with the operating mechanism for the movable contact member 34: of the main switch 34 as indicated schematically by the chain lines. The stator element 37a is provided with distributed grooves in which are installed coils 21a, 21b and 22a, 22b with coils 21a22a, Zita-22b lying diametrically. Coils 21a, 2112 each including a rectifier 49 in series therewith, are connected in parallel between the mercury pool cathode 35a and the ignition pin 35b of current gate 35. Similarly, coils 22a, 2212 each including a rectifier 59 in series therewith, are connected in parallel between the mercury pool cathode 36a and ignition pin 36b of current gate 36. Anode 35c is connected to cathode 36a, and anode 36c is connected to cathode 35a thus to establish the anti-parallel arrangement. These current gates are thus of the ignitron type but can be of some other type so long as they are able to provide a gating function.

Rotation of the rotor 37b of impulse generator 37 induces voltages in the stator coils 21a, 21b and 22a, 22b and these induced voltage impulses function to ignite and hence render conductive the respective current gates 35, 36 with which they are associated. The duration of these induced voltage impulses depends upon the magnitude of the pole arc of the rotor 37b in that each coil is induced so long as the pole of the rotor runs past it. Each pair of coils 21a, 22a and 21b, 2211 are induced together so that both current gates are always controlled at the same time. Which of the two current gates is finally ignited depends upon the polarity of the alternating current just then present on the one or the other gate. Coils 21a, 21b and 22a, 2212 are laid into precisely distributed grooves in the stator 37a so that current gates 35, 36 are controlled as to conduction within definite time divisions of a switch-over operation. More about this will be said later in connection with an explanation of the manner in which the device operates. By mechanically coupling the rotor 37b of impulse generator 37 with the actuating mechanism for the movable contact member 340 of the main switch 34, one thus obtains a very accurate control for the current gates or valves 35, 36 in relationship to specific phase positions of the overall switching operation.

The invention includes further switches having movable contact members which likewise are mechanically coupled with the actuating mechanism for the movable contact member 34c of the main switch 34 so that these are likewise operated in a definite time relationship to operation of switch 34. These include a commutation switch 38 having stationary arcuate contact segments 3&1, 33b and a movable contact member Sfic. Also included is a resistance switch 39 consisting of two sections or poles each of which is represented by a stationary arcuate contact segment 3%, 3% and a movable contact member 39c, 39:! respectively. The movable contact members 390, 35%! are so designed that in their end positions, as shown in the drawing, they do not make contact with the stationary contact segments 39a, 3%. Engagement between contacts takes place in intermediate positions during movement of main switch contact member 34c. Further included is a current gate switch 42 consisting of two series connected sections, and each section is constituted by a pair of arcuate contact segments 42a, 42b and a movable contact member 42c. The movable contact members of these switches i.e. contact members 33c, 39c, 39d, 420 are mechanically coupled with the actuating mechanism for movable contact member 34c of main switch 34 as indicated by chain lines. The apparatus further includes a pre-selector switch 4% having a movable contact 490 and stationary contacts 4%, 45%, and a. resistance element 41.

As to commutation switch 38, contact 3&1 is connected to rail 32, contact 3812 is connected to rail 33 and contact 380 is connected to anode 35c and hence also to cathode 36a.

As to double-pole resistance switch 39, contact 353a is connected to rail 32, contact 3% is connected to rail 33, contact 39c is connected llO contact 4% of pre-selector switch 40, and contact 39d is connected to the other contact 4%. One end of resistance 41 is connected to contact 40c and the opposite end of this resistance is connected to the movable contact 340 of main switch 34.

As to the current gate switch 42, stationary contacts 42a, 42b of the upper section are connected to contact 380 and hence also to anode 35c and cathode 36a, movable contact 420 of this upper section is connected to stationary contacts 42a, 42b of the lower section and movable contact 420 of this lower section is connected to cathode 35a and anode 36c which are also connected to the movable contact member 34c of the main switch 34.

These electrical circuit connections which have been described above is thus such that the movable switchover contact member 34c of the main switch 34 leads, on the one side across current gates 35, 36 wired anti-parallel, and commutation switch 38 to one of the contact rails 32, or 33, and on the other side the switch-over contact 340 can likewise be switched across resistance 41 and preselector switch 40 as well as the double pole resistance switch 39, all series connected, to the one or the other of the two rails 32, 33. The connection is made, however,

only during the switching over process, since the contacts of resistor switch 39 are open at all other times, i.e. when the movable contacts 39c, 39d occupy their end positions. Thus resistance 41 carries current only within a very short switch-over time. The contacts of the switches 42 which lie parallel to the anti-parallel connected current gates 35, 36 are closed in their idle or terminal positions 1 and 12. By mechanically coupling the contacts 420 so as to be operated simultaneously with operation of the contacts of the main switch 34, contacts 420 are separated from their contacts 42a, 42b only during a definite time period within one switch-over operation. Within this time period, the current gates 35' and 36 take over the task of carrying current. The voltage necessary for ignition of the current gates arises upon opening of the contacts of the current gate switch 42, with arcs starting up on them. The

total voltage drop anising here must be greater than the ignition voltage of the current gates.

The are voltage drop appearing on one, two or more current gate switches 42 wired in cascade forms the transistory operational voltage on the current gates as long as these are not yet conductive. The arcs are extinguished at the moment of ignition of the current gates.

The circuit arrangement of FIG. 1 operates in the following manner:

For any given tap connection on the transformer windin 31, such as tap 3 10, current flows from this tap across the slidable contact member 32a and rail 3-2 to stationary contact 34a of the main switch 34 and thence through the movable contact member 340 engaged therewith to the line connection 51. This circuit is shown in heavy lines. Preselecto-r switch 4t), which is not mechanically coupled with the main switch 34 for operation with the latter, has its movable contact 48c now engaged with stationary contact 401:. When the drive mechanism 43 for the tap changing operation is first started, movable contact 340 separates from contact 34a at position 2. Current can no longer pass through the main switch 34 but it is enabled to take a by-pass circuit to the line connection 51 through the still closed contacts 38a, 3550 of commutation switch 33 and the still closed contacts 42a, 42c of the current gate switches 42. Resistance switch contacts 3%, 39d close at time point 3 to thus connect resistance 41 to the next tap step 31d through rail 33 and slidable contact member 33a. The voltage that exists between transformer taps 3llc and 31d is thus applied across resistance 41 and there is established a current connection from the movable contact of the main switch 34 to the transformer winding tap 31d to which the load is to be connected by the tap changing operation. Through this section of the winding 31 bridged over temporarily, there flows across the contacts of the current gate switches 42, and later across one of the two current gates 35 or 36, a temporary circulation current limited by resistance 41. The ignition pins 35b, 36b of the current gates 35, 36 receive one ignition impulse each across winding 21a and 22a of impulse generator 37 which is driven by the same actuating mechanism 43. The time course of the ignition pulse is shown in the time diagram 18 correlated to angular movement of the generator rotor 37b. In the time from 1-4 takes place the starting of the generator rotor 37b to full velocity which is reached at moment 4 and (thus also at this moment the maximal impulse voltage induced in coils 21a, 21b and 22a, 22b is presented to the ignition pins of the current gates. During the time 4-6, the impulse generator 37 provides this maximal voltage to the ignitionpins. The time are 1-6 corresponds to the width of the pole of the generator rotor and is equal to one half the pole arc angle a. During the impulse voltage, the contacts of (the two current gate switches 42 wired in series open at point 5. Thereby an arc of about 20 volts each arises at each contact opening point. The are voltages, added together are used to supply the current gates 35, 36, connected in anti-parallel, the necessary anode volt-age to effect current conduction to their respective cathodes. One or the other of the two current gates thus becomes conductive, depending upon the direction of the voltage impressed between the anodes and cathodes. The ignition impulse ceases afiter passing of moment 6, and the next passage of the voltage through Zero causes the then open current gate to close. Thereupon, commutation switch 38 is switched over at points 7, 8 in a current-free condition from engagement between contacts 38a, 380 to engagement between contacts 38c, 38b and thus establish a connection through to winding tap 31d. The movable contacts 420 of the two sections of switch 42 then engage stationary contacts 42b, point 9, to close a by-pass from tap 31d through switches 38 and 42 to line 51. At moment 10, contact 39d leaves contact 39!) to open the shunt circuit through resistance 41. Finally, switch contact 34c will reach contact 34b, at point 11 to connect tap 31:! directly of it.

In the same manner, but in the reversed direction of movement of the rotor of impulse generator 37 and of the movable contact members of the several switches, further tap changing can be made to take place, either back to tap 31c, or in switching further to tap 31c. The positions of the contacts shown in FIG. 1 and of the time points in the time diagram 18 relate of course to one direction of rotation of the several switch contacts and of the rotor 37b of generator 37, i.e. clockwise, with the starting position at 1.

The impulse generator 37 is constructed fundamentally like a synchronous generator. The impulse ignition coils for rendering the current gates conductive are installed in grooves in the stator with a prescribed angular distribution. The laminated stator body can be provided with only the number of grooves necessary to receive the necessary number of coils, or a stator body with grooves distributed throughout its periphery can be used, the coils being in serted in the proper grooves and the remainder of the grooves being left empty. The rotor 37b with pronounced poles can be of the permanent magnet type, as shown, or a rotor with an exciter winding thereon for producing the necessary magnetic flux can be utilized.

Each directional movement of the various switch contact members and impulse generator rotor is of course coordinated to one tap changing operation. Correspondingly, coils 21a or 211;, 22a or 22b bring about the ignition effect of the current gates each time.

The start-up of the rotor of impulse generator 37 must take place within a very short time, i.e. within the are 1-4 in time diagram 18 corresponding to the armature position. Thus there is required a large amount of driving power or in the alternative, the rotor must have as small a mass as is practical. On the other hand, for control of the current gates, a definite minimum output is necessary. If the rotor of the impulse generator has a small mass and hence a comparatively small voltage inducing effect in the stator coils, a pre-amplifier is preferably inserted in advance of the connections to the ignition pins of the current gates. Suitable for this are gas-discharge tubes, or switch transistors.

In the embodiment of FIG. 1, the contacts of resistance switch 39 will not operate entirely spark-free when switched to the closed position. The modification shown in the embodiment of FIG. 2 enables switch 39 to also operate spark-free, and for this purpose another set of anti-parallel connected current gates 44, 45 are provided, these gates being connected in series with the resistance element 41 and switch 39. Ignition of one or the other of current gates 44, 45 takes place only after the contacts of the double pole resistance switch 39 have been closed, thus when the contacts of this switch have moved from position 1 to position 3 indicated on the switch.

For providing the necessary voltage ignition impulses for the current gates 44, 45, the stator 37a of the impulse generator is provided with additional coils 46a, 47a and 46b, 47b. These coils with series arranged rectifiers are connected between the ignition pins 44b, 45b and the pool cathodes 44a, 45a, respectively of the gate valves 44, 45. Moreover, in this embodiment, the current gates 35, 36 require additional voltage impulse coils in the stator 37a and these are indicated at 21c, 22c and 21a, 22d. As with the other ignition coils, these latter coils also include series arranged rectifiers. The coils denoted by the letters b and d function to provide the ignition voltage impulse on the return movement of the armature element 37b. Their relative distribution in the stator 37b is indicated in FIG. 2. The time diagram 18 shows ignition of the current gates 35, 36. These are ignited twice during each tap-changing operational sequence. The time diagram for ignition of the current gates 44, 45 is shown at 19. The four current gate arrangement according to FIG. 2 as contrasted with the two gate arrangement of FIG. 1 operates arc-free on closing of the switch-over contacts of switch 39, and consequently is free from contact erosion.

The operational sequence for the modified construction according to FIG. 2 is as follows, with the impulse moments entered in time diagrams 18, 19, as well as the momentary switch positions from l-15 corresponding to one complete tap changing operation.

Previous to an actual change in the taps under load, the preselector switch 40 is shifted from its previous position to the one shown in FIG. 2 wherein movable contact 460 is engaged with stationary contact 46b. The movable contact 34c of the main switch 34 leaves stationary contact 34a at time point 2 and current which had been flowing through the main switch to line 51 is now by-passed in the shunt circuit across commutation switch 38 and the current gate switch 42 to line 51. Resistance switch contacts 39b, 39d close at point 3 shown on this switch. The current gates 35, 36 each now receive an ignition impulse at time point 4-7 in the diagram 18. Switch contacts 420 leave stationary contacts 42a, at point 6 on these switches, and one of the current gates 35, 36 begins to carry current. The current gates 44, 45 now receive ignition voltage impulses, time points 5-11 in time diagram 19. One of these latter two current gates then becomes conductive. That part of winding 31 between taps 31c and 31d is now closed over resistance 41 and a circulation current fiows. This circulating current will continue as long as the ignition impulse over the current gates 35, 36 lasts, and then in the next passage through zero of the alternating current in winding 31 the ignited current gate is extinguished at moment 8 at the latest. Commutation switch 38 now switches in an arcfree manner, the circuit with the current gates 35, 36 to the next tap 31a, points 8 to 9. Current gates 35, 36 now receive ignition voltage impulses a second time and one of these two gates will then conduct current, from moment 10 to 13. The resistance 41, in the next passage of the alternating current through zero after the end of the ignition voltage impulse, point 11, is switched off across current gates 44, 45. The movable switch contacts 420 engage stationary contacts 42b and thus extinguish current gates 35, 36 time point 12 of this switch 42. Resistance switch contact 3% then becomes disengaged from contact 39d at time point 14 on this switch. The movable contact 340 of main switch 34 now engages with stationary contact 34b, at time point 15 on this switch and comes to a stop at point 16, thus completing one tap changing operation.

In conclusion, while two embodiments of the invention have been illustrated and described, various modifications may be made therein in the construction and arrangement of parts without, however, departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. Apparatus for switching over from one tap to another on a transformer winding while under load comprising a load switch having a line connected contact movable between a pair of stationary contacts, connectable respectively to dilferent taps on said transformer winding, first and second current by-pass circuits extending from said movable contact to each of said stationary contacts, said first by-pass circuit including a commutation switch having a contact movable between a pair of stationary contacts connected respectively to said stationary contacts of said load switch, said movable contact of said commutation switch being connected in series with a pair of anti-parallel arranged impulse voltage controlled current gates and a current gate switch having movable and stationary contacts connected in parallel with said current gates, said second by-pass circuit including a resistance element connectable by a preselector switch in series with either of two sets of movable and stationary contacts of a resistance switch, said contact sets of said resistance switch being connected respectively to said stationary contacts of said main switch, a voltage impulse generator for providing said current gates with voltage impulses to render said current gates alternatively conductive, said generator including rotor and stator elements one of which is provided with magnetic field producing means and the other with coils for the production of impulse voltages upon rotation of said rotor, said coils along with rectifiers arranged in series therewith being connected between the cathodes and control electrodes of said current gates, and an actuating means common to said load switch, commutation switch, current gate switch and resistance switch for actuating the movable contacts of those switches as Well as the rotor of said impulse generator in coordinated relation such that upon switching said main switch from one tap to another, the load current is caused to flow temporarily through said by-pass circuits.

2. Apparatus as defined in claim 1 for changing taps on a transformer winding under load and which further includes a second pair of anti-parallel arranged impulse voltage controlled current gates connected in series in said second by-pass circuit, said stator of said impulse generator being provided with additional coils for the production of impulse voltages and which together with rectifiers arranged in series therewith are connected between the cathodes and control electrodes of said second pair of current gates for rendering them alternately conductive and non-conductive for closing said second by-pass circuit subsequent to closure of the contacts of said resistance switch and for opening said second by-pass circuit prior to re-opening the contacts of said resistance switch No references cited. 

1. APPARATUS FOR SWITCHING OVER FROM ONE TAP TO ANOTHER ON A TRANSFORMER WINDING WHILE UNDER LOAD COMPRISING A LOAD SWITCH HAVING A LINE CONNECTED CONTACT MOVABLE BETWEEN A PAIR OF STATIONARY CONTACTS, CONNECTABLE RESPECTIVELY TO DIFFERENT TAPS ON SAID TRANSFORMER WINDING, FIRST AND SECOND CURRENT BY-PASS CIRCUITS EXTENDING FROM SAID MOVABLE CONTACT TO EACH OF SAID STATIONARY CONTACTS, SAID FIRST BY-PASS CIRCUIT INCLUDING A COMMUTATION SWITCH HAVING A CONTACT MOVABLE BETWEEN A PAIR OF STATIONARY CONTACTS CONNECTED RESPECTIVELY TO SAID STATIONARY CONTACTS OF SAID LOAD SWITCH, SAID MOVABLE CONTACT OF SAID COMMUTATION SWITCH BEING CONNECTED IN SERIES WITH A PAIR OF ANTI-PARALLEL ARRANGED IMPULSE VOLTAGE CONTROLLED CURRENT GATES AND A CURRENT GATE SWITCH HAVING MOVABLE AND STATIONARY CONTACTS CONNECTED IN PARALLEL WITH SAID CURRENT GATES, SAID SECOND BY-PASS CIRCUIT INCLUDING A RESISTANCE ELEMENT CONNECTABLE BY A PRESELECTOR SWITCH IN SERIES WITH EITHER OF TWO SETS OF MOVABLE AND STATIONARY CONTACTS OF A RESISTANCE SWITCH, SAID CONTACT SETS OF SAID RESISTANCE SWITCH BEING CONNECTED RESPECTIVELY TO SAID STATIONARY CONTACTS OF SAID MAIN SWITCH, A VOLTAGE IMPULSE GENERATOR FOR PROVIDING SAID CURRENT GATES WITH VOLTAGE IMPULSES TO RENDER SAID CURRENT GATES ALTERNATIVELY CONDUCTIVE, SAID GENERATOR INCLUDING ROTOR AND STATOR ELEMENTS ONE OF WHICH IS PROVIDED WITH MAGNETIC FIELD PRODUCING MEANS AND THE OTHER WITH COILS FOR THE PRODUCTION OF IMPULSE VOLTAGES UPON ROTATION OF SAID ROTOR, SAID COILS ALONG WITH RECTIFIERS ARRANGED IN SERIES THEREWITH BEING CONNECTED BETWEEN THE CATHODES AND CONTROL ELECTRODES OF SAID CURRENT GATES, AND AN ACTUATING MEANS COMMON TO SAID LOAD SWITCH, COMMUTATION SWITCH, CURRENT GATE SWITCH AND RESISTANCE SWITCH FOR ACTUATING THE MOVABLE CONTACTS OF THOSE SWITCHES AS WELL AS THE ROTOR OF SAID IMPULSE GENERATOR IN COORDINATED RELATION SUCH THAT UPON SWITCHING SAID MAIN SWITCH FROM ONE TAP TO ANOTHER, THE LOAD CURRENT IS CAUSED TO FLOW TEMPORARILY THROUGH SAID BY-PASS CIRCUITS. 